Patent flower is fine wheat flour
Patent flower is suitable for the finer Bakwerk (biscuits, cake). It is flour that is made from the inner of the flour body of wheat, but a lot finer ground and sieved to normal flour. When you have a recipe where flour is in, the general is meant to be the normal wheat flour. Patent flower is the most white flower, this comes through the extra grinds and the sieves. Patenbloem is also called American wheat flour, the difference is in the ratio of starch and gluten proteins.